Avalanche Forecast

Northwest Coastal

Date issued

Dec 15, 2017 - 4:55 PM

Valid until

Dec 16, 2017 - 2:00 PM

Prepared by

swerner

Saturday is storm day! Avoid avalanche terrain during periods of heavy loading from rain, new snow and wind.

Regular season
Friday - December 15, 2017
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Below Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Saturday - December 16, 2017
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Sunday - December 17, 2017
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

New storm slabs will likely build through the forecast period on all aspects and elevations. Wet loose avalanches may occur from steeper terrain features below treeline.

Travel and Terrain Advice
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • The new snow will require several days to settle and stabilize.

Avalanche Problem 2: Deep Persistent Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Weak layers buried near the base of the snowpack can't be dismissed while new snow or rain load the surface.

Travel and Terrain Advice
  • Avoid areas with overhead hazard.
  • Take extra caution around areas with a thin or variable snowpack.

Avalanche Summary

On Friday, wet slab avalanches size 1-2 were reported from steep terrain where the ground cover consists of smooth rock slab features. These avalanches went to ground. Widespread natural avalanche activity expected through the forecast period with new rain, snow and wind.

Snowpack Summary

Up to 30 mm of precipitation fell as a rain and saturated the snowpack up to 800 m on Thursday. On Friday, the freezing levels dropped and the new snow is currently building storm slabs on all aspects and elevations.

Below the surface sits a well-settled snowpack overlying several layers of interest. Down 70-100 cm you'll likely find a 5-10 cm thick crust which was buried on November 23 and in some areas, a feathery surface hoar layer down 50-60 cm producing moderate snowpack test results. The widespread crust/facet interface that was buried at the end of October can now be found 100-200 cm deep and exists region wide.

Weather Forecast

Saturday: Snow amounts 20-30 cm. Alpine temperatures -2 and freezing levels 800 m. Ridgetop winds strong from the southwest.

Sunday: Cloudy with sunny periods and new snow amounts 3-10 cm. Alpine temperatures -3 and freezing levels 600 m. Ridgetop winds light with strong gusts from the southwest.

Monday: Cloudy with isolated flurries. Alpine temperatures -3 and freezing levels 600 m. Ridgetop winds light from the southwest.

Check out the Mountain Weather Forecast for more detail.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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